Modified freeform fabricated part and a method for modifying the properties of a freeform fabricated part

ABSTRACT

The present invention is a process for modifying the properties of a porous freeform fabricated part by increasing its density and reducing its porosity. The porosity and density of a freeform fabricated part are altered by packing the pores in a freeform part with an infiltrant, such as a preceramic polymer. The process includes drawing a vacuum on or pressurizing the freeform part while it is in an infiltrant bath, thereby forcing the infiltrant into the pores of the freeform part. After removing the densified freeform part from the infiltrant bath, the freeform part is subjected to a treating process, such that the infiltrant within the pores transforms to a ceramic or ceramic-containing phase to thereby increasing the density of the freeform part.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. patent application, Ser. No.: 09/847,136,filed May 2, 2001, now abandoned which is a divisional of U.S. patentapplication Ser. No.: 09/311,771, filed May 13, 1999 now U.S. Pat. No.:6,228,437, issued on May 8, 2001, which is a continuation-in-part (CIP)of U.S. patent application, Ser. No. 09/220,922, filed Dec. 24, 1998 nowabandoned, the entirety of which is incorporated herein by reference.

TECHNICAL FIELD

This invention relates to freeform fabricated parts and in particular,to a method for modifying the properties of a freeform fabricated partby increasing its density.

BACKGROUND ART

As a result of the demand for ways to improve manufacturing efficiencyand the need for rapid prototype development, freeform fabrication hasbecome a popular method for manufacturing parts. Freeform fabricationoriginated with a process called stereolithography wherein a focussedultra-violet laser scans the top of a bath of a photopolymerizableliquid polymer plastic material, thereby causing the top of the bath andthe area just below the surface to polymerize. The polymerized layer isthereafter lowered into the bath and the laser scanning process isrepeated until a second polymerized layer is formed. As the secondpolymerized layer forms, it bonds to the first layer. This process isrepeated until a plurality of superimposed layers form the desired part.The shape of the part is first designed in a computer aided designsystem (i.e., a CAD/CAM system), which is linked to the machineperforming the stereolithography process. Most freeform fabricationprocesses include a computer aided design system for coordinating theexecution of the freeform fabrication process. In the case ofstereolithography, the laser beam scans the area of the bath necessaryto form the freeform fabricated part (hereinafter referred to as“freeform part”) designed on the computer aided design system.

The ability to produce an actual part directly from a design providesmany advantages. One advantage includes eliminating the timetraditionally used to develop the necessary tooling to manufacture thefreeform part. Another advantage includes reducing the amount ofmachining, such as grinding, milling, drilling, etc., required tocomplete the part because the freeform fabrication process produces asubstantially readily usable final product. Minimizing the amount ofhands-on machining, therefore, translates into reducing the amount ofpotential human error and increasing efficiency. The amount of timesaved in preparing for manufacturing also makes the freeform fabricationprocess attractive for rapid prototype development, which has been oneof the main interests surrounding this technology in recent years. Thebenefit of rapid prototyping includes the ability to manufacture variousconfigurations in a short amount of time, thereby providing designerswith actual models of their designs.

Another method of freeform fabrication includes a technique calledThree-Dimensional Printing (3DP), which consists of depositing apowdered material (e.g., a powdered ceramic, powdered metal, powderedplastic, or combination thereof) in sequential layers, one on top of theother. After depositing each layer of powdered material, a liquid binderis selectively supplied to the layer of powdered material using a typeof ink-jet printing technique in accordance with a computer model of thethree-dimensional part being fabricated. Following the sequentialapplication and binding all of the required powder layers, the unboundpowder is removed, thereby resulting in the formation of the designedthree-dimensional part.

A third method of freeform fabrication includes Selective LaserSintering (SLS). SLS includes a process whereby a powder dispenserdeposits a layer of powdered material into a target area. A lasercontrol mechanism, which typically includes a computer that houses thedesign, modulates and moves the laser beam to selectively sinter a layerof powder dispensed in the target area. Specifically, the controlmechanism operates to selectively sinter only the powder disposed withinthe defined boundaries of the design. The control mechanism operates thelaser to selectively sinter sequential layers of powder, producing acompleted part comprising a plurality of layers sintered togetheryielding the completed design.

A fourth method of freeform fabrication includes Ballistic ParticleManufacturing (BPM). BPM uses an ink-jet printing apparatus wherein anink-jet stream of liquid polymer or polymer composite material is usedto create three-dimensional objects under computer control, similar tothe way an ink-jet printer produces two-dimensional graphic printing.The device is formed by printing successive cross-sections, one layerafter another, to a target using a cold welding or rapid solidificationtechnique, which causes bonding between the particles and the successivelayers.

An additional freeform fabrication technique, includes Fused DepositionModeling (FDM). FDM consists of building solid objects in a layeringfashion from polymer/wax compositions by following the signals producedby a computer aided design system. Specifically, FDM builds structuresby extruding a fine filament of plastically deformable material througha small nozzle. The computer aided design system appropriately directsthe nozzle over a build surface in the x, y and z directions, therebycreating a three-dimensional object that resembles the design.

Another method of freeform fabrication includes a technique calledPhotochemical Machining, which uses intersecting laser beams toselectively harden or soften a polymer plastic block. The underlyingmechanism used is the photochemical cross-linking or degradation of thematerial. U.S. Pat. No. 5,490,962 provides a detailed summary of each ofthe above mentioned freeform fabrication techniques and is herebyincorporated by reference.

The specific processes described above as being suitable for formingproducts of the present invention are inherently free of fiberreinforcement. In the main, these processes result in the manufacture orproduction of a freeform based on particulate material. As distinct fromthe prior art directed to making preforms, articles made by the presentinvention do not use fiber reinforcement and therefore are fiber free.

The methods described above, however, often result in the fabrication ofa porous freeform part, thereby creating undesirable mechanicalproperties for the freeform part. A freeform part having inadequatestrength, unsatisfactory hardness, low temperature tolerance, lowabrasion resistance, rough surface finish, poor bonding of individuallayers or poor bonding of powder particles within the layers presents asignificant limitation to the types of applications in which freeformparts can be utilized. Therefore, what is needed is a means forincreasing the mechanical, thermal or other physical properties offreeform parts.

DISCLOSURE OF INVENTION

The present invention exploits the porosity of a freeform fabricatedpart by packing the pores of a freeform part with an infiltrant that iscapable of transforming to a ceramic or a ceramic-containing phase. Theinfiltrant comprises a preceramic polymer, which is selected to bondwith the freeform part such that the resulting composition improves themechanical, thermal and other characteristics of the freeform part.Packing the pores of the freeform part, therefore, increases its densityand concomitantly decreases its porosity. Particularly, increasing thedensity of the freeform part increases one or more or all of thefollowing properties: mechanical strength, hardness, temperatureresistance, abrasion resistance, thermal conductivity, and erosionresistance. These properties may be enhanced by carefully fabricatingthe freeform part such that a certain porosity is imparted, selectingparticular infiltrants with various concentrations that add the desiredproperties to the freeform part, and repeating the infiltration processuntil the desired density is achieved.

Accordingly, one aspect of the present invention is a process formodifying the properties of a porous freeform part comprising the stepsof depositing a porous freeform part in an infiltrant bath, drawing avacuum on the porous freeform part and the infiltrant bath such that theinfiltrant enters the pores within the freeform part, and removing thedensified freeform part from the infiltrant bath. The infiltrant isnormally a preceramic polymer that is capable of transforming to aceramic or a ceramic-containing phase. Furthermore, the preceramicpolymer is preferably a polymer capable of nanocrystalline ceramic phasegrowth such that the preceramic polymer can enter the pores within thefreeform part. Upon being removed from the infiltrant bath the densityof the freeform part increases because the previously empty pores nowcontain infiltrant, and the infiltrant within the pores of the freeformpart transforms to a ceramic or a ceramic-containing phase. Subjectingthe freeform part to multiple infiltration processes further decreasesthe porosity of the freeform part and concomitantly increases itsdensity.

A second embodiment of the present invention includes pressurizing theinfiltrant as an alternative to or in conjunction with drawing a vacuumon the porous freeform part and the infiltrant bath such that theinfiltrant enters the pores within the freeform part.

A third embodiment of the present invention includes heating theinfiltrant while pressure is being applied.

A fourth embodiment of the present invention includes placing the porousfreeform part in a vacuum dessicator, applying a vacuum and allowing aninfiltrant to enter the vacuum dessicator such that the infiltrantenters the pores within the freeform part.

A fifth embodiment of the present invention includes subjecting thedensified freeform part to a series of post-processing steps upon beingremoved from the infiltrant bath such that the infiltrant within thepores of the densified freeform part transforms to a ceramic or aceramic-containing phase. The post-processing steps may include one ormore or all of the following steps: curing the infiltrant, heating theinfiltrant at a rate, duration and temperature such that the infiltranttransforms to a ceramic or ceramic-containing phase within the pores ofthe freeform article, annealing the transformed infiltrant and coolingthe freeform fabricated part and the transformed infiltrant.

A still further embodiment of the present invention includes a freeformfabricated part having pores therein comprising a ceramic or aceramic-containing phase disposed within a portion of the pores with thefreeform part.

The foregoing features and advantages of the present invention willbecome more apparent in light of the following detailed description ofexemplary embodiments thereof as illustrated in the accompanyingdrawings.

BEST MODE FOR CARRYING OUT THE INVENTION

Through conducting a series of experiments, the inventor of the presentinvention recognized that infiltrants such as preceramic polymers, whichare inorganic or organic polymers that transform to ceramic whensubjected to intense heat, are capable of infiltrating the pores of afreeform part. The inventor of the present invention also recognizedthat increasing the density of the freeform part with certaininfiltrants improved the mechanical characteristics of the freeformpart, which serves as a support structure for the infiltrants.Therefore, the present invention is a process comprising the steps offabricating a freeform part, depositing the freeform part in aninfiltrant bath, drawing a vacuum on the porous freeform part and theinfiltrant bath such that the infiltrant enters the pores of thefreeform, and subjecting the freeform part and infiltrant to a treatingprocess that may include one or more post-processing steps. Freeformparts for use in practicing the method of the present invention werefabricated using a three-dimensional printing technique similar to thatdescribed in U.S. Pat. Nos. 5,204,055 and 5,340,656 and 5,387,380, whichare hereby incorporated by reference. Although the freeform parts inthese experiments were made using the three-dimensional printingtechnique, the present invention may be used with freeform parts made byvirtually any known freeform fabrication technique such asstereolithography, selective laser sintering, fused deposition modeling,ballistic particle manufacturing, and photochemical machining. It ispreferable that the freeform parts be capable of withstanding the typeof post-processing steps associated with transforming an infiltrant to aceramic or ceramic-containing phase. Three different types of freeformparts were fabricated using the three-dimensional printing technique.One was a ¼ inch by ¼ inch by 4 inch Acrysol bonded silicon carbide(SiC) part. Specifically, silicon carbide powder, manufactured byWashington Mills under the tradename SIKA I, was bonded by the organicbinder Acrysol WS-24, which is an acrylic colloidal dispersionmanufactured by Rohm & Haas. The second type of freeform part was a ¼inch by ¼ inch by 1½ inch alumina part. In that instance, brown aluminumoxide (Al₂O₃) powder manufactured by Norton Company under the productcode 7131 was bonded by the same Arysol WS-24 binder. The third type offreeform part was also a ¼ inch by ¼ inch by 1½ inch alumina partfabricated using the same brown aluminum oxide (Al₂O₃) powdermanufactured by Norton Company mentioned above using thethree-dimensional printing technique. However, this third type offreeform part was fabricated using the inorganic binder, colloidalsilica (SiO₂), manufactured by the Norton Company under the tradenameNyacol. Although the three freeform-fabricated parts used in ourexperiments were manufactured using silicon carbide and aluminum oxide,other materials such as metal, ceramic and metal-ceramic compositescould be manufactured using the three-dimensional printing technique.Additionally, organic and inorganic binders other than Arysol WS-24 andcolloidal silica could be used in the three-dimensional printingprocess.

The original density of the three types of parts was about thirtypercent (30%) to about thirty seven percent (37%). In other words, sixtythree percent (63%) to about seventy percent (70%) of thethree-dimensional fabricated freeform part was porous. Therefore, it mayalso be preferable to subject the freeform part to post-processingmethods, such as mild sintering or annealing, but doing so only improvesthe density to about thirty eight percent (38%) to about thirty-nine(39%). In the method of the present invention, the density of a freeformpart is increased by depositing the freeform part into an infiltrantbath consisting of a preceramic polymer (i.e., ceramic precursor), whichcan be an organic or inorganic polymer but is generally in the form ofan inorganic polymer. Any preceramic polymer capable of transforming toa ceramic or a ceramic-containing phase having nanocrystallinestructures therein may be used as an infiltrant. Although the preceramicpolymers used in all of the following examples were in the form of aliquid or a sol-gel, the preceramic polymer could be in a number ofother forms, such as an organic solvent based solution or a liquiddispersion containing solid particles. In the latter case, the liquidprovides a medium to deliver particles into the pores of a fabricatedfreeform part.

TABLE 1 Variable No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 Infiltrant AluminaBlack-glas ™ poly(methyl Perhydrido Tyranno Polyalu- sol-gel siliconvinylsilane) polysilazane Coat ™ minosilazane oxycarbide (PMVS) (PHPS)Polysilazane (PAS) Vacuum 5 × 10⁻³ torr 5 × 10⁻³ torr 5 × 10⁻³ torr 5 ×10⁻³ torr 5 × 10⁻³ torr 5 × 10⁻³ torr Pressure Vacuum 5 to 60 min 5 to60 min 5 to 60 min 5 to 60 min 5 to 60 min 5 to 60 min Time CompositionAir or Nitrogen or Argon Air, Nitrogen or Nitrogen of Curing oxygenargon Nitrogen or argon Atmosphere argon Curing 110° C. 85° C. 150 to250° C. 100° C. 110° C. 80 to 200° C. Temperature Curing Time 2 hours 5to 12 1 to 3 hours 1 to 3 hours 1 to 3 hours 1 to 3 hours hoursComposition Air or Nitrogen or Argon Air or Nitrogen or Nitrogen ofConvert- oxygen argon Nitrogen or argon ing Atmos- argon phere Initial110° C. 100° C. 250° C. 150° C. 150° C. 150° C. Converting TemperatureRate of 2 to 10° C./ 2 to 10° C./ 2 to 10° C./ 2 to 10° C./ 2 to 10° C./2 to 10° C./ Increasing min min min min min min Converting TemperatureFinal 1000° C. 1000° C. 1000° C. 1000° C. 1000° C. 1000° C. ConvertingTemperature Composition Air or Nitrogen or Argon Air, Nitrogen orNitrogen of Anneal- oxygen argon Nitrogen or argon ing Atmos- argonphere Annealing 1000 to 1000 to 1000 to 1000 to 1000 to 1000 toTemperature 1600° C. 1600° C. 1800° C. 1800° C. 1800° C. 1800° C.Annealing 1 to 8 hours 1 to 8 hours 1 to 8 hours 1 to 8 hours 1 to 8hours 1 to 8 hours Time Rate of 10° C./min 10° C./min 10° C./min 10°C./min 10° C./min 10° C./min Cooling

Referring to Table 1, the freeform parts were deposited in the followingpreceramic polymers: alumina sol-gel, silicon oxycarbide(SiOC),poly(methylvinylsilane) (PMVS), perhydridopolysilazane (PHPS),polysilazane, and poly(aluminosilazane). Other potential preceramicpolymers that could be used as infiltrants include polysilane,polycarbosilazane, poly(borosilazane), polysiloxane and polycarbosilane,and other molecularly mixed polymers that are capable of producingnanocrystalline ceramics or metals or mixtures hereof. Variouspolysilanes, polysilazanes, silicon oxycarbide (SiOC),polycarbosilazane, polysiloxarie, perhydridopolysilazine andpolycarbosilanes are commercially available. The alumina sol-gel used inExample 1 was prepared using a known process. The silicon oxycarbide(SiOC) used in Example 2 is produced by Allied Signal under thetradename Blackglas. The Blackgasä silicon oxycarbide (SiOC) actuallyconsists of a monomer solution, Blackgasä 489A, and a catalyst,Blackglasä 489C, which are combined before the freeform-fabricated partis deposited into such a bath The perhydridopolysilazane used in Example4 is sold by Tonen, and the polysilazane used in Examples 5 isdistributed by UBE under the tradename Tyranno Coat. Although apoly(methylvinylsilane), a poly(aluminosilazane) or a poly(borosilazane)may not be manufactured on a commercial scale, it is known how tomanufacture such preceramic polymers. Particularly, when using apoly(methylvinylsilane), it is preferred to use a reactive endblockedpoly(methylvinylsilane) as described in a Final Technical Reportentitled Novel Precursor Approaches for CMC Derived by Polymer Pyrolysisdated Feb. 15, 1994 prepared under Government Contract No.F49620-91-C-0017 and/or a Final Technical Report entitled A Study of theCritical Factors Controlling the Synthesis of Ceramic Matrix Compositesfrom Preceramic Polymers prepared under Government Contract No.F49620-87-C-0093, which are both hereby incorporated by reference. Thepoly(methylvinylsilane) preceramic polymer was synthesized using amodified sodium-coupling reaction of component chlorosilanes to producea family of reactive endblocked polymers. In particular,vinyldimethylsilyl end groups are incorporated into the polymerstructure to retain desirable curing, ceramic conversion and stabilitycharacteristics. Dimethylsilyl and methylenedimethylsilyl groups arealso incorporated into the polymer structure to increase flexibility ofthe polymer backbone and to increase the synthetic yield of the polymer.In general, the poly(methylvinylsilane) polymers produce carbon-richsilicon carbide ceramic materials upon thermal conversion. Also, whenusing a poly(aluminosilazane) as a preceramic polymer, it is preferredto produce such poly(aluminosilazane) using the method as described in aFinal Technical Report entitled Silcon-Based Nanostructural CeramicsDerived from Polymer Precursors. Development of Processing, Structure &Property Relationships prepared under Government Contract No.F49620-95-C-0020 and/or in an article entitled Aluminum-27 andSilicon-29 Solid State Nuclear Magnetic Resonance Study of SiliconCarbide/Aluminum Nitride Systems: Effect of Silicon/Aluminum Ratio andPyrolysis Temperature in Chemistry of Materials (1998). Single-sourcepoly(aluminosilazane) precursors were prepared by reactingbexamethylcyclotrisilazane and triethylaluminum either neat or with bothcomponents dissolved in dry hexane at room temperature, using standardprocedures for handling pyrophoric and air-sensitive materials. Networkpolymer compositions were designed by varying the ratio of the startingreactants. Physical properties of the resulting polymers also dependedon the ratio of the starting reactants. The poly(aluminosilazane)precursors produce homogeneous blends of nanocrystalline siliconcarbide, aluminum nitride and silicon nitride ceramics or solidsolutions upon thermal conversion.

Continuing to refer to Table 1, individual freeform parts were depositedinto a vacuum dessicator that contained each infiltrant. Although eachinfiltrant, other than the Tyranno Coatä polysilazane, was not asolution, it is possible to add a solvent to each infiltrant, therebydecreasing its concentration. Reducing the viscosity of the infiltrantin order to increase pore penetration by the infiltrant in the freeformpart may be a viable reason for using a solvent to form a solution.After being deposited in the infiltrant bath, a vacuum is drawn on thefreeform parts ranging from about 100 (torr) to about 5×10⁻³ (torr). Inthese experiments, each freeform part and infiltrant were vacuumpressurized at a pressure of about 5×10⁻³ (torr) for about five minutesto about sixty minutes. The time required to infiltrate the firstfreeform part with the infiltrant varied with each infiltrant because ofthe varying infiltrant viscosity and pore size. Upon packing (e.g.,filling) at least a portion of the pores in the first freeform partswith the infiltrant, the freeform part, packed with infiltrant, wasremoved from the vacuum dessicator and cured, which increased theviscosity of the infiltrant such that the freeform parts retained theinfiltrant within its pores. In these examples, all infiltrants werethermally cured, which is one method of radiation curing. Otherradiation curing techniques include x-ray, microwave, visible orultraviolet light, and electron beam radiation. Depending upon thecomposition of the infiltrant, it is also possible to chemically curethe infiltrant. For example, the Blackgasä silicon oxycarbide (SiOC) maycure by a chemical curing process without any external heat, due to thecombination between the Blackglasä 489A and the Blackgasä 489C. Applyingheat to the Blackglasä silicon oxycarbide (SiOC), however, reduces thecuring time. Therefore, it is preferred to heat the Blackgasä siliconoxycarbide (SiOC) to a temperature of about 85° C. for about five tosixty minutes according to the manufacturer's recommendation. Asmentioned above, the infiltrant can also include a solvent, but if so,the solvent must be removed from the infiltrant and freeform part priorto or during the curing stage.

After curing the infiltrant, the freeform part was placed in an O-ringsealed, fused silica tube (hereinafter referred to as “tube”), whichcontrolled the temperature, atmosphere and pressure used in performingthe converting stage. The tube was only capable of withstanding atemperature of about 1000 degrees Celsius. Therefore, the freeform partwas transferred to a ceramic tube, such as an alumina or mullite tubebefore elevating the temperatures above about 1000 degrees Celsius.Depending upon the infiltrant's sensitivity to air, the composition ofthe atmosphere may include argon or nitrogen in order to maximize thetransformation of the infiltrant to the desired ceramic orceramic-containing phase. The converting stage comprises applying heatto the infiltrant and freeform part such that the infiltrant transformsto a ceramic or a ceramic-containing phase and bonds to the freeformpart. Although it is preferred to increase the temperature of theatmosphere within the tube at a rate of about two degrees Celsius perminute (2° C./min) until the temperature of the atmosphere attains aboutone-thousand degrees Celsius (1000° C.), it is possible to perform theconverting stage by raising the temperature at a faster rate ranging upto about ten degrees Celsius per minute (10° C./min).

In all instances, the freeform parts were also annealed by keeping theparts within the tube after the converting stage was complete andholding the temperature of the tube constant within a range of aboutone-thousand degrees Celsius (1000° C.) to about one-thousand eighthundred degrees Celsius (1800° C.) for about one hour to about eighthours. Annealing the infiltrant increases its crystalinity and initiatesadditional ceramic grain formation such that the density of the freeformpart further increases. Finally, the freeform parts were cooled at apreferred rate of about ten degrees Celsius per minute (10° C./min)until the freeform part attained ambient conditions. It is also possibleto cool the freeform part at a rate ranging from about two degreesCelsius per minute (2° C./min) to about ten degrees Celsius per minute(10° C./min).

Referring to Table 2, the resulting composition varied depending uponthe material of the freeform part and the infiltrant.

TABLE 2 Coupon Part Resulting Material Infiltrant Composition Al₂O₃Alumina sol-gel Al₂O₃/Al₂O₃ Al₂O₃ Blackglas ™ SiOC/Al₂O₃ Siliconoxycarbide Al₂O₃ poly(methylvinyl-silane) SiC(+C)/Al₂O₃ (PMVS) Al₂O₃Perhydridopolysila-zane SiO₂(with air)/ (PHPS) Si₃N₄(+Si)/Al₂O₃ Al₂O₃UBE Si₃N₄(+Si)/Al₂O₃ Tyranno Coat ™ Polysilazane Al₂O₃Polyaluminosilazane SiC/AlN/Si₃N₄/Al₂O₃ (PAS) SiC Alumina sol-gelAl₂O₃/SiC SiC Blackglas ™ SiOC/SiC Silicon oxycarbide SiCPoly(methylvinyl-silane) SiC(+C)/SiC (PMVS) SiC Perhydridopolysila-zaneSiO₂ (with air)/ (PHPS) Si₃N₄(+Si)/SiC SiC UBE Tyranno Coat ™Si₃N₄(+Si)/SiC Polysilazane SiC Polyaluminosilazane SiC/AlN/Si₃N₄/SiC(PAS)

Although certain infiltrants may have destroyed a portion of theinter-particle bonds formed during the three-dimensional printingprocess, such as dissolution of the bond between an organic based binderand the three-dimensional printed part, the density of the resultingcomposition surpassed the density of the original freeform part.Specifically, upon undergoing the infiltration process described hereinand infiltrating the freeform part with Blackgasä silicon oxycarbide(SiOC), poly(methylvinylsilane) (PMVS) Perhydridopolysilazane (PHPS),Tyranno Coat™ Polysilazane, and Polyaluminosilazane (PAS), the densityof the freeform part increased to about fifty percent (50%) to aboutsixty percent (60%). The density of the freeform part infiltrated withthe alumina sol-gel increased to about forty percent (40%) to aboutforty-five (45%).

The infiltration process of the present invention, therefore, decreasedthe porosity and increased the density of the freeform part. The densityof each freeform part is further increased and its porosity furtherdecreased upon repeating the process until the desired density andporosity are achieved. It is beneficial to practicing the process of thepresent invention to first engineer the porosity of the freeform part toreceive the infiltrants. Specifically, by fabricating freeform articleshaving an adaptable porosity, varying the type of infiltrant,controlling the concentration of the infiltrant and subjecting thefreeform part to various and multiple infiltration processes, one canmanipulate the porosity and mechanical characteristics of a freeformarticle such that a freeform part having desired properties of hardness,strength and density is produced.

An alternate process for modifying the properties of a porousfreeform-fabricated part comprises the further step of pressurizing theinfiltrant after drawing a vacuum on infiltrant and freeform part. Thispressurizing step increases the potential of packing the pores in thefreeform part with the infiltrant.

Another alternate process comprises the steps of depositing anindividual freeform part in a vacuum dessicator containing an infiltrantand pressurizing the infiltrant rather than drawing a vacuum. Regardlessof whether a vacuum is drawn on the infiltrant and freeform part, it mayalso be beneficial to heat the infiltrant as pressure is being appliedin order to initiate curing of the infiltrant within the pores of thefreeform part.

Still another alternate process for modifying the properties of a porousfreeform part comprises placing the freeform part in an empty vacuumdessicator, drawing a vacuum on the freeform part and then introducingan infiltrant into the vacuum dessicator such that the infiltrant entersthe pores within the freeform part.

Although the invention has been described and illustrated with respectto the exemplary embodiments thereof, it should be understood by thoseskilled in the art that the foregoing and various other changes,omissions and additions may be made without departing from the spiritand scope of the invention.

What is claimed is:
 1. A densified freeform-fabricated fiber free partproduced by the process of: (a) providing a porous fiber free freeformfabricated part and depositing said part into a bath comprising aninfiltrant which includes a ceramic precursor or ceramic containingphase and wherein said ceramic or ceramic containing phase originatesfrom a precursor selected from the group consisting of polysilane,polysilazane, silicon oxycarbide (SiOC), poly(methylviylsilane),poly(aluminosilazane, perhydridopolysilazane, poly(borosilazane),polycarbosilazane, poly(siloxane), poly(carbosilane) and mixturesthereof (b) infiltrating the porous freeform fabricated part such thatthe infiltrant enters at least a portion of the pores resulting in adensified freeform fabricated part; and (c) removing the densifiedfreeform fabricated part from the bath.
 2. A densified freeformfabricated part, comprising: (a) a fiber free freeform fabricated parthaving pores therein; and (b) a ceramic or a ceramic containing-phasecontained within a portion of said pores, and wherein said ceramic orceramic containing phase originates from a precursor selected from thegroup consisting of polysilane, polysilazane, silicon oxycarbide (SiOC),poly(methylvinylsilane), poly(aluminosilazane), perhydridopolysilazane,poly(borosilazane), polycarbosilazane, poly(siloxane), poly(carbosilane)and mixtures thereof.
 3. The freeform-fabricated part of claim 2 whereinthe freeform fabricated part is either a metal, ceramic or a mixturethereof.